Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

Thu
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

Santa said he would deliver a few inches of snow to the NW Mountain forecast area today. Any accumulating snow will add more volume for dry loose avalanches on steep, northerly facing terrain. In those areas, be ready to manage these sluffs, especially if you are riding in sustained steep terrain where they can accumulate mass. An old persistent slab avalanche problem also exists on some previously wind-loaded terrain features. These slabs will become harder to visually see and identify once they become buried by a little new snow. 

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    Since 12/9, several northwest-to-southwest wind events formed slabs around a foot thick or more in heavily wind-loaded terrain features. These wind-drifted slabs are most commonly found at higher elevations below leeward ridgelines and rollovers on east to northeast-facing terrain. They can also be found around the northern half of the compass in a few concave terrain features that collect drifting snow, such as gullies. These slabs are often hard and difficult to trigger, but some formed over weak, faceted snow that is slow to heal, making for variable feedback.  Assess recent wind-loading patterns and consider avoiding previously wind-loaded terrain features, especially in high-consequence terrain. 

    A booming collapse and shooting cracks triggered on 12/21 on this heavily drifted slope demonstrate the potential to trigger a hard, persistent slab avalanche.  

  • Loose Dry

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–1.5

    In terrain that has been protected from the sun and wind, most commonly on the north-to-east aspects, you can find a snowpack that is weak and cohesionless.  In these areas, you can trigger dry loose avalanches in terrain steeper than 35 degrees.  Point-release instabilities are relatively small and easy to recognize. Still, they can spell trouble by pushing you into trees, rocks, or gullies, especially in long, steep terrain where they will gouge to the ground and gain more volume.  Use sluff management techniques or move to less consequential, lower slope angles to manage the problem. If you are in an area that receives 2 to 4 inches of new snow accumulating today, be prehard for these sluffs to become notably larger and more difficult to manage. 

    Skier triggered dry loose avalanches on Schuylkill Ridge. 12/19.

Avalanche Discussion

We have two subtle condition changes occurring that may turn out to be fairly notable. Those are the increasing volume for dry loose avalanches or sluffs, and those old persistent slabs becoming harder to recognize.

Let's start with the dry loose avalanches. These sluffs have occurred for some time as the December drought faceted away our snowpack, leaving a pile of weak snow available for entrainment. Here are some examples over the last couple of weeks (Snodgrass, Schuylkill Ridge, Axtell, Emmons, Elk Creek). These sluffs have all been small and relatively easy to manage. However, it is important to note that as new snow accumulates, the size and volume of these sluffs will begin to become increasingly more difficult to manage. Perhaps those changes will begin today if Santa delivers some snow, or we may have to wait for the next storm. By some point later this week, we should begin to see enough new snow accumulate that this avalanche problem will transition into a new soft slab avalanche problem. 

The subtle change occurring with the current persistent slab avalanche problem is the visual clues to this problem beginning to disappear. Once a little fresh snow accumulates over these old hard slabs and previously wind-loaded terrain features, they will be harder to recognize. The surface of the snow will look soft, and that could be misleading to what's below. If you are traveling in what should be previously wind-loaded terrain, keep these decreasing visual clues in mind. The latest in our steady trickle of feedback from our persistent slab problem comes from Mt. Emmons on Sunday, right on the boundary between our two forecast zones.   The second rider, crossing a wind-loaded feature on the far looker's left side of Red Lady Bowl, popped a hard slab that broke 1 or 2 feet deep near the ground.  Although our slab issues are localized to previously wind-loaded terrain features, like a wind slab, we've been calling it a persistent slab due to its unusually prolonged period of instability. A hybrid problem, if you will. These slabs started forming earlier this month as multiple wind-drifting events over the very weak snowpack created by the December drought.  Other recent feedback includes collapses on Anthracite Mesa yesterday, below Schuylkill Peak on Saturday (video), and a skier-triggered slab Friday on Mt. Tilton.  

Regions covered